Corrosion inhibitors



Patented Aug. 9, 1949 STATES ram orrics CORROSION INHIBITORS of New Jersey No Drawing. Application February 26, 1946. Serial No. 650,391

6 Claims. (Cl. 252-75) This invention relates to the protection of metals from corrosion by aqueous systems. More particularly, it pertains to a new and useful group of compounds which inhibit the corrosion of polymetallic systems in contact with water and aqueous alcoholic solutions.

Liquid cooling systems such as automotive cooling systems, heat exchangers, shock absorbers and hydraulic presses usually contain parts made of iron, brass, copper, aluminum, solder and other metals. It is well known that water and aqueous alcoholic solutions exert a corrosive action on these metals which results in the discoloration, roughening and pitting of the surface of the metals and the formation of corrosion products which either cling to the metals with consequent reduction of heat transfer efiiciency or slough off and settle at points of low fluid velocity causing clogging of the system.

Many attempts have been made to reduce the corrosive action of the contact liquid. Small additions of alkali metal salts of monochromate and dischromate have for example, been tried for the purpose of inhibiting corrosion of the metallic iron. In order to counteract corrosion of zinc, iron and copper, it has been proposed that sodium benzoate be dissolved in the liquid. The addition of these compounds resulted in some instances in-more serious corrosion than if the inhibitor had been omitted, because under normal circumstances in the absence of an inhibitor corrosion would have been of a general character rather than localized. The alkali metal chromate or dichromate will inhibit the corrosion of the brass, copper, aluminum, solder and other metals in contact with liquids.

It is still a further object of my invention to provide a corrosion inhibitor which can be conveniently added to polymetallic systems. Only a small quantity of my corrosion inhibitor is necessary to prevent corrosion of all of the metals present.

In accordance with this invention it has been found that if a small quantity of an alkali metal thereof and Z-methyl, 2-amlno-propanol-1 is added to water or an aqueous alcoholic solution there results a solution which does not readily corrode polymetallic systems comprising iron, aluminum, brass, copper, solder and other metals. Either after the addition of these ingredients or simultaneously with them, if necessary, sufilcient alkali is added so that the resultant solution has an initial pH of about 10. Alkali as referred to above and hereinafter includes alkali metal hydroxides and carbonates. It is presently found that adjusting the pH to about 10 afiords maximum corrosion inhibition in various polymetallic systems. The quantity of alkali required is dependent upon the acidity of liquid medium being treated. The addition of these materials to water or an aqeous alcoholic solution in contact with a polymetallic system prevents the corrosion oi all of the metals present even after heating at 65 C. for a year, as shown in Example 1.

The solutions with which my inhibitor may be used include water and aqueous solutions containing at least one alcohol such as ethanol, propanol or other mono-hydroxy alcohols, or the polyhydroxy alcohols such as ethylene glycol, propylene glycol, diethylene glycol, and glycerlne.

Only small quantities of each material are necessary to provide a proper inhibiting action; considerable variation in concentration of the inhibitor is permissible depending upon the contact liquid used. A suitable range by weight of the liquid isfrom about 0.25% to 1.00% of an alkali metal chromate. about 0.25% benzoic acid or an alkali metal salt thereof and 1.25% 2-methyl, Z-amino-propanol-l.

It is to be further understood that the term, alkali metal chromates, as herein used includes such obvious chemical equivalents as alkali metal dichro-mates. For example, an alkali metal chromate can be formed in situ in the liquid medium by adding an alkali metal dichromate and an alkali. In this case one mole of an alkali metal dichromate reacts with two equivalents of alkali to produce two equivalents of the chromate. A corrosion inhibitor in which the components have been varied would consist, for example, of 0.25% to 1.00% sodium dichromate, 0.25% sodium benzoate and 0.50% to 0.75% 2-methyl, 2-aminopropanol-l. An inhibitor in which benzoic acid had been substituted would be for example 0.25% to 1.00% sodium chromate, 0.25% benzoic acid and 0.50% to 0.75% Z-methyl, z-amino-propanol-l. An example of a mixture in which two components are substituted would be 0.25% to chromate. benzoic acid or an alkali metal salt 1.00% sodium dichromate, 0.25% benzoic acid 'ponents and the combination of any two.

me sages and 0.50% to 0.25% 2-methyi, 2-amino-pro= panel-1. The pH of the solution of inhibitors shown previously is adjusted with alkali so that the operating pH of the inhibitor is about 10. All percentages are based on the metric volume of the aqueous system. It has also been found that succinic acid can be substituted for benzoic acid in these reactions with equally efiective results.

The mixtures described in this invention inhibit corrosion to an extent impossible to obtain with any one of the components alone or any binary combination of them. Corrosion tests were conducted in the apparatus described in Example 1 using aqueous solutions of each of the com- The results of these experiments are tabulated below:

Inhibit! Results Corrosion oied es of aluminum and etch ng oi copper.

Formation of nodules on cast iron and local corrosion. Corrosion oi copper.

Corrosion of iron and aluminum.

Pitting oi aluminum near iron.

1 0.26% sodium chromste 2 0.25% 2-msthyl-2-amino-propanol-l.

I 0.257 sodium chromste 0.25? sodium benzoate 4 0.26% 2-methyl-2-amino-propanol-l. 0.25% sodium cbromate The following examples illustrate a method of carrying out the present invention, but it is to be understood that these examples are given by way of illustration and not 01 limitation.

Example 1 inch apart by copper wire which was steel bolted to'the aluminum branch and soldered to the copper branch. There was limited access of air to the system. This apparatus was submerged in the contact liquid which contained the inhibitor to be 50 tested. The system was maintained at room temperature approximately ten hours a day with no stirring and the remainder of the time the system was maintained at 65 C. and mechanically stirred. Tests were continued for a period of a year. During this time there was substantially 5 no indication of corrosion of any of the metals and substantially no sludge formation.

Example 2 About 0.25% of sodium chromate, 0.25% of suc cinic acid, and 1.20% of 2-methyl, 2-amino-propanol-l are added to tap water. This solution was subjected to the same test conditions as used in Example v1 for a year at which time substane5 tialiy no corrosion of the metals was noted.

Example 3 About 0.25% of sodium chromate, 0.25% ben- Example s About 0.25% of sodium chromate, 0.25% benzoic acid and 0.75% z-methyl. 2-amino-propanol- 1 are added to an aqueous solution of half ethylene glycol and half tap water by volume. This solution was subjected to the same test conditions as used in Example 1 for a year at which time no corrosion of the metals was observed.

Modifications may be made in carrying out the present invention without departing from the spirit and scope thereof and the invention is to be limited only by the appended claims.

I claim: I

1. The process of inhibiting the corrosion of metals in polymetallic systems when said metals are in contact with an aqueous system, selected from the class consisting of water and aqueous alcohol which comprises adding to said aqueous system a corrosion inhibitor consisting of: a chromium containing salt selected from the group consisting of the alkali metal chromates and the alkali metal dichromates in amounts ranging from 0.25% to 1.00%; an organic acid selected from the group consisting of benzoic acid and succinic acid in amounts ranging from 0.10% to 0.25%; 2-methyl, 2-amino-propanol-1 in amounts ranging from 0.50% to 1.25%; and alkali in an amount sumcient to provide a pH of about 10 in said aqueous system; said percentages being based on the 'metric volume of said aqueous system.

2. The process of inhibiting the corrosion oi metals in polymetallic systems when said metals are in contact with an aqueous system selected from the class consisting of water and aqueous alcohol which comprises adding to said aqueous system a corrosion inhibitor consisting of: 0.25%

of sodium chromate, 0.25% benzoic acid and 0.75% 2-methyl, 2-amino-propanol-1; said percentages being based on the metric volume of said aqueous system.

3. The process of inhibiting the corrosion of metals in polymetaliic systems when said metals are in contact with an aqueous system selected from the class consisting oi water and aqueous alcohol which comprises addingto said aqueous system a corrosion inhibitor consisting of: 0.25% of sodium chromate, 0.25% succinic acid and 1.20% 2-methyl, 2-amino-propanol-1: said percentages being based on the metric volume of said aqueous system.

4. A non-corrosive liquid consisting of an aqueous system selected from the class consisting 5 of water and aqueous alcohol and a corrosion inhibitor therefor consisting of: a chromium containing salt selected from the group consisiing of the alkali metal chromates, "and the alkali metal dichromates in amounts ranging from 0.25% to 1.00%; an organic acid selected from the group consisting of benzoic acid and succinic acid in amounts ranging from-0.10% to 0.25%; 2-methyl, 2-amino-propanol-1 in amounts ranging from 0.50% to 1.25%; and alkali in an amount sumcient to provides pH of about 10 in said aqueous system: said percentages being based on the metric volume of said aqueous system.

5. A non-corrosive liquid consisting of an aqueous system selected from the class consisting zoic acid and 0.75% 2-methyl, 2-amino-propanol- 7 of water and aqueous alcohol and a corrosion 1 are added to an aqueous solution of half ethanol and half tap water by volume. The test described in Example 1 was continued for one year with substantially no indication of corrosion of the metals present.

inhibitor therefor consisting of: 0.25% sodium chromate; 0.25% benzoic acid, and 0.75% Z-methyi. 2-amino-propanol-1; said percentages being based on the metric volume of said aqueous 7 system.

6. A non-corrosive liquid consisting of an aqueous system selected from the class consisting of water and aqueous alcohol and a corrosion inhibitor therefor consisting of: 0.25% sodium chromate; 0.25% succinic acid, and 1.20% 2-methy1, 2-amino-propano1-1; said percentages being based on the metric volume of said aqueous system.

JOHN A. ELDER, JR.

REFERENCES CITED The following references are of record in the file of this patent:

Number Number UNITED STATES PATENTS Name Date Calcott et a1 Mar. 1, 1932 Dana et a1. Jan. 22, 1935 Clapsadle et a1 Aug. 9, 1938 Hass et a1 Dec. 6, 1938 Weber July 22, 1941 FOREIGN PATENTS Country Date Great Britain Jan. 27, 1927 

